1. Field of the Invention
The present invention relates to radioelectrophotography process for recording image information carried by radiation.
2. Description of the Prior Art
As one process for recording radiation images, there is a process called "xeroradiography" which uses light-sensitive materials for electrophotography, in addition to the ordinarily employed processes using silver halide photographic light-sensitive materials.
As one example of a xeroradiographic process, there is the process employing xerography and irradiating with X-rays instead of visible light to obtain a latent image comprising an electric charge distributions of X-ray-irradiated areas and non-irradiated areas, as described in U.S. Pat. No. 2,666,144.
As another example of a xeroradiographic process, there is the process utilizing a fluorescent substance or the like as an auxiliary substance in the above-described process in order to supplement the weak radiation absorption efficiency of the light-sensitive layer, and irradiating an electrophotographic light-sensitive material with radiation and the visible light emitted by the fluorescent substance as described in U.S. Pat. No. 2,856,535.
Final images are formed by subjecting the latent images obtained by the above processes to toner development or by transferring the thus formed toner images to a resin plate or the like, or by conducting toner development after transferring the latent images to a resin plate or the like.
However, as compared with the sensitivity of silver halide materials, the sensitivity of radioelectrophotographic materials used in such processes is so low that they are employed with difficulty except in certain radiophotographic procedures (e.g., "mammography").
On the other hand, as one radioelectrophotographic process providing high sensitivity, there is the process described by Reiss (hereinafter referred to as the "Reiss chamber process") in Zeitschrift fur Angevandte Phiski, vol. 19, ppl-4 (Feb. 19, 1965) which comprises using as one electrode a metal plate capable of emitting electrons upon irradiation and as another electrode a metal plate, and irradiating an insulating film inserted in the gap between the electrodes while applying a high voltage across the electrodes, thereby forming latent images on the insulating film surface.
In this process, electrons emitted by radiation ionize gas during traveling between the electrodes to remarkably increase the number of electric charges, and the electrons thus increased in number attach to the insulating film to form a latent image. Therefore, there can be expected higher sensitivity as compared with the aforesaid xeroradiography. However, changes in the distance of the gap between the electrodes across which the voltage is applied cause great changes in the electron-amplifying ratio (i.e., sensitivity), the gap between the electrodes must be maintained narrow, and, in addition, the gap must be maintained constant, at least in the area greater than image area to be formed. This process is difficult to practice.
A process analogous to the above-described Reiss chamber process is the process described in Japanese Patent Application (OPI) No. 82,791/73 (hereinafter referred to as the "Xonics process"). This process comprises using an ordinary metal electrode in place of a metal electrode capable of emitting electrons as is employed in the Reiss chamber process, irradiating to directly discharge in the gas between electrodes, and adhering generated ions onto an insulating film to form a latent image.
In this process, a gas of a higher atomic nubmer such as Xe, Kr, etc., is held in the gap between the metal electrodes at atmospheric pressure or above to improve the efficiency of radiation absorption, and the generated ions are adhered to an insulating film. Therefore, similarly with the aforesaid Reiss chamber process, there can be expected higher sensitivity as compared with xeroradiography. However, to maintain the gap distance between the electrodes is technically difficult, and, in addition, it is difficult to maintain the electrodes parallel since the gap is held at atmospheric pressure or above (at least the electrode on the side struck with X-rays is liable to undergo bending or the like since its thickness must be thin in order to minimize the absorption of X-rays) and, in addition, there is the problem of introducing the gas into the gap between the electrodes and the problem of the gas-discharging means. Thus, this process lacks practical utility. When the pressure of the gas is increased to raise the sensitivity, these defects become greater.